SONET and T-carrier are both synchronous TDM.
But T-carrier does not use atomic clock. Why does SONET?
Is it because SONET does not use buffer? But how does it prevent bit loss if there is no buffering?
Network Engineering Stack Exchange is a question and answer site for network engineers. It only takes a minute to sign up.Sign up to join this community
SONET, or rather the synchronous digital hierarchy it's running on, requires very tight clock coupling across the whole structure. In order to stay within the sub-millisecond tolerances, there's no other way than with atomic clocks.
Sharing a central clock wouldn't work due to the inherent limitation of the speed of light, which covers just 300 km in one ms (or only 200 km over fiber) - minus processing overhead, the hierarchy would need to be very limited in geographic size.
T-carrier uses a much simpler master-slave clocking, so there's no requirements for atomic clocks.